417
FXUS65 KTFX 161728
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1028 AM MST Sun Nov 16 2025

Aviation Section Updated.

.KEY MESSAGES...

- Patchy dense fog near the Milk River Valley thins out later
  this morning, but may redevelop again tonight into Monday
  morning.

- Passing weather systems will bring periods of light mountain
  snow and lower elevation scattered rain and snow showers Monday
  through Wednesday.

- Temperatures cool closer to average by the middle and end of the
  week.

&&

.UPDATE...
/Issued 841 AM MST Sun Nov 16 2025/

Minor adjustments were made to the near-term precipitation chances
in southwest Montana based on trending observations and the latest
hi-res model guidance.

Otherwise, dense fog continues along the Milk River Valley with
visibilities down to a quarter mile being reported in Havre.
Patchy fog has also started develop along the Hwy 87 corridor in
Chouteau county with Fort Benton reporting 2SM. With visibilities
maintaining at Fort Benton and Big Sandy, there is no current need
to expand the Dense Fog Advisory.

For the Milk River Valley, hi-res guidance still suggests that
the worst of the fog will be over by around 11 AM. However, there
is some suggestion in the models that patchy dense fog could
continue into the early afternoon for some portions of the Hi-
Line. At this point in time there is not enough confidence to
extend the advisory but this situation will be monitored closely
in case conditions fail to improve.

Additionally, there is a chance for fog to redevelop along the
Hi-Line this evening into the overnight hours. For now, no
products will be issued for tonight just yet as confidence is not
quite high enough. But there is, once again, a potential for dense
fog along the Hi-Line east of Shelby.   -thor


&&

.DISCUSSION...
/Issued 841 AM MST Sun Nov 16 2025/

 - Meteorological Overview:

Weak southwesterly flow aloft develops today and tonight,
resulting in an increase in mid- and higher level cloudiness for
all areas with scattered areas of rain showers and some light
mountain snow developing along the Continental Divide and over
Southwest Montana. Winds will generally be on the light side and
will combine with lingering surface moisture for nighttime and
early morning patchy fog development over the next couple of days,
mostly near the Milk River Valley.

Periods of lower grade, mostly mountain rain and snow will
continue along and ahead of a weak Pacific trough due to pass
through the Northern Rockies sometime on Wednesday. H700
temperatures remain around -5C before falling to around -10C near
the trough axis. Theoretically, this would bring snow levels down
to the valleys and the plains on Wednesday, but precipitation
amounts look negligible by then.

Another trough moves into the western CONUS for the second half
of the workweek, but the main low pressure center looks to shear
off towards the southwestern CONUS, leaving drier conditions for
the state of Montana. The upper level jet moves over the Northern
Rockies Friday into next weekend and sends a broad trough that
will bring periods of mountain snow and a return to windy
conditions. - RCG

 - Forecast Confidence & Scenarios:

Nighttime and morning patchy fog development over the next couple
of days...

Nocturnal and morning patchy fog development looks to be most
widespread near the Milk River Valley for the next couple of
nights. Higher cloud cover is currently disrupting the fog, but
this should be temporary with the fog returning again near dawn. A
dense fog advisory was sent out through 11 am today since most of
the visibility reductions were concentrated along and near US
highway 2. The fog thins out later today, but there is around a
50% chance for visibility falling below a half mile in this area
again tonight into Monday morning.

Periods of light mountain snow and lower elevation rain and snow
showers Monday through Wednesday...

Rain and snow associated with an approaching Pacific weather
system looks to be light and scattered in nature. Temperatures
aloft don`t look to be very favorable for accumulating snow until
later Wednesday when the precipitation is winding down.

Increasing winds and opportunities for mountain snow heading into
next weekend and wintry weather looking to return Thanksgiving
week...

Drier conditions move in for the second half of the workweek with
the next Pacific trough progged to move towards the southwestern
CONUS. Winds increase again heading into next weekend while
mountain snow returns along the Continental Divide. Lower
elevation precipitation will be limited by the downsloping effect
of the deep layer westerly flow. A growing number of ensemble
suites are hinting at a series of colder and more productive
troughs moving through the Northern Rockies during the week of
Thanksgiving. This will be closely monitored given volume of
travel heading into the holiday weekend. - RCG

&&

.AVIATION...
16/18Z TAF Period

Patchy dense fog and low CIGS were slowly dissipating across the
Milk River Valley in North Central Montana this morning, with this
trend expected to continue through the early afternoon hours;
however, few to scattered LIFR/IFR CIGS may linger over/near the
KHVR through the mid-afternoon hours. Elsewhere mid- to upper level
cloudiness was increasing from south to north, with this trend
expected to persist through the 1618/1718 TAF period as
southwesterly flow aloft ushers in additional moisture. Isolated to
scattered light precipitation, mainly over the mountains of
Southwest Montana and along the Continental Divide, will obscure
peaks. Confidence remains high that MVFR conditions, if not
LIFR/IFR, will once again develop at the KHVR terminal after 17/07z
due to fog and/or low CIGS; with increasing confidence that these
conditions will expand further west towards the KCTB terminal
through this timeframe. - Moldan

The KWYS TAF will not be issued until airport operations resume
next spring.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  39  60  36 /  10  10  10  30
CTB  52  33  57  30 /   0  10  10  20
HLN  56  36  56  35 /  10  10  20  30
BZN  58  34  55  33 /  20  10  20  30
WYS  48  30  41  27 /  60  50  70  50
DLN  56  34  53  32 /  20  10  20  20
HVR  51  31  52  30 /   0  10  10  20
LWT  59  37  57  31 /  10  10  10  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 11 AM MST this morning for Hill County-
Northern Blaine County.

&&

$$
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